1. Field of the Invention
This invention relates to an image reading apparatus for reading the image of an original, such as a scanner, a copier or a facsimile apparatus, and particularly to an original cover provided in these apparatuses.
2. Description of the Related Art
FIG. 7 of the accompanying drawings is a schematic view showing the construction of a color image reading apparatus.
The letter P designates an original to be read placed on an original glass stand 100, and a contact image sensor 101 is scanned in parallelism to the original glass stand 100 to thereby read an image on the original.
The contact image sensor 101, as schematically shown in FIG. 8 of the accompanying drawings, has incorporated therein LED's 101R, 101G and 101B of three colors which are light sources for irradiating the original, a rod lens array 101L for imaging the reflected light from the original on the light receiving element of an image sensor 101S, and the image sensor 101S. The light sources of three colors are successively changed over and turned on, and the image sensor 101S reads the reflected light of each color from the original to thereby effect color resolving and reading.
The contact image sensor 101, as shown in FIG. 7, is fixedly supported on a slider 102 sliding on a guide shaft 103 fixed to the main body of the apparatus. Also, a belt 104 for transmitting motive power from a motor 105 which is a scanning drive source is fixed to the slider 102. By the forward and reverse rotation of the motor, the contact image sensor 101 is capable of reciprocally scanning within the range of the original glass stand 100.
The constituent elements of the image reading apparatus include, besides those elements described above, an electrical equipment portion 106 comprising a control board and an electric power source. These constituent elements are disposed in a cover 110 for fixedly supporting the original glass stand 100.
On the original glass stand 100, an original cover 111 for pressing the original against a glass plate is openably and closably mounted with the fitted portion of a recess 110a formed in the rear end portion of the cover 110 and the convex portion 111a of the rear end portion of the original cover as a fulcrum. Also, an original pressure sheet 112 comprising a sheet material 112a and a sponge 112b is stuck on the inner surface of the cover which is opposed to the original glass stand 100.
FIG. 9 of the accompanying drawings is a read image data processing block diagram by the image reading apparatus. An image output signal read by the image sensor 101S in synchronism with the LED's successively turned on and off is sent to an amplifier 121 and is amplified thereby, and thereafter is converted into a digital image signal by an A/D converter 122.
The A/D converter divides the dynamic range of the image sensor (the reading output difference between the pure while portion and the inky-black portion of the original) into the bit number thereof and allots the number of gradations in conformity with the brightness of the image on the original.
For example, when an A/D converter having resolving power of 8 bits is used, white to black can be discriminated into 256 gradation levels, and in the case of an A/D converter having resolving power of 10 bits, white to black can be discriminated into 1024 gradation levels.
Accordingly, in an image reading apparatus using an A/D converter of 8 bits, in the color reading by light sources of three colors R, G and B, 24 bits=about 16,700,000 colors can be discriminated, and in the case of an A/D converter of 10 bits, 30 bits=about 1,074,000,000 colors can be discriminated.
There are several kinds as the output forms of the image signal of the image reading apparatus, and an output form suitable for the use of a read image can be selected.
When a writing is to be read and the substance thereof is to be applied to OCR or when a monochromatic drawing is to be read, a monochromatic binary image is suitable therefor, and use is made of image data obtained by transforming an image signal obtained by turning on e.g. only G of the light sources of R, G and B into a binary value by a certain threshold value in an image processing circuit incorporated in a gate array 123.
When an image is to be read with a view to read such as image as a photograph and output it to a monochrome printer, use is made of image data obtained by transforming the image signal also by the G light source into a binary value by the use of halftone processing such as the dither method or the error diffusion method.
When the processing of a color image is to be effected, multivalue (24 bits, etc.) image data is suitable therefor.
The image signal passed through the above-mentioned image processing circuit is outputted to an apparatus 200 such as a personal computer through an interface circuit 124.
In the case of the related art as described above, however, the following problem has arisen.
An image scanner comprising the above-described construction makes the most of the features of a contact image sensor and is very compact and light in weight and therefore, there is one which, as shown in FIGS. 10A and 10B of the accompanying drawings, is vertically placed with one side thereof underlaid by the use of an accessory stand 300 and is made usable even in this state. Originals which can be scanned with the scanner vertically placed are limited to sheet-like originals, and an original cover and the fore end of the apparatus are made closable by a sucker or the like and an original is scanned while being urged against the glass plate.
On the other hand, the original cover in the construction of the related art is opened and closed by the pivotal movement thereof about a fulcrum at the rear end thereof, but in such system, it cannot press a thick original such as a book. Generally, the original cover is adapted to slide in a vertical direction to thereof cope with a thick original.
In such an image scanner, however, if the hinge construction as described above is used, the hinge is opened when the scanner is vertically placed and the original cover floats from the glass plate and becomes incapable of pressing an original and therefore, use could not be made of a hinge for coping with a thick original.